1. Field of the Invention
The present invention relates to a lens driving apparatus for a taking lens of a camera or the like, a lens guiding mechanism, and an optical instrument equipped with a taking lens and the like.
2. Related Background Art
A power-changing mechanism and a focusing mechanism are necessary for carrying out zooming in a taking lens for a camera or the like. If these mechanisms are made independent from each other, then a lens driving system comprising a lens driving motor, a lens position detecting device, and the like is needed for each mechanism, thus making it necessary to provide two lines of driving systems. This has been a great obstacle to reducing the size and cost of optical instruments such as camera.
In view of these disadvantages, as described in Japanese Patent Application Laid-Open No. HEI 5-249362, there has been proposed an optical instrument in a zoom taking optical system comprising a front group lens and a rear group lens, in which a holder barrel for the front group lens and a driving ring for moving it along the optical axis are connected to each other by means of a helicoid, a holding member for the rear group lens engages a cam groove formed in the inner periphery of the driving ring, and the driving ring is rotated, so as to move the front group lens together with the holder barrel and move the rear group lens along the cam groove.
The cam groove of this optical instrument has a flat region orthogonal to the optical axis and an oblique region not orthogonal thereto. The oblique region of the cam groove is used for moving the rear group lens upon a focus switching operation, whereas the flat region of the cam groove is used so as not to move the rear group lens upon a focusing operation. Using such a cam groove, this optical instrument is intended to carry out focus switching and focusing by use of a single driving source.
In the above-mentioned optical instrument, however, it is necessary that the driving ring be rotated about the optical axis upon focusing. Therefore, the technique of such an optical instrument is not applicable to those moving the rear group lens without rotating the driving ring or those having no driving ring.
As those moving the rear group lens without rotating the driving ring or those having no driving ring, on the other hand, lens driving mechanisms having a lens barrel with a quadrangular cross section have been known as described in Japanese Utility Model Registration No. 2548509 and Japanese Patent Application Laid-Open No. HEI 9-222550. These lens driving mechanisms, however, do not disclose any power-changing and focusing operations by use of a single driving source and driving mechanism. There has also been a desire for developing a technique capable of carrying out power-changing and focusing operations by use of a single driving source and driving mechanism in these lens driving mechanisms having a lens barrel with a quadrangular cross section and the like.
Further, there has been a desire for developing a technique for reducing the size and cost of optical instruments by carrying out power-changing and focusing operations by means of a single driving source and driving mechanism in a lens driving mechanism having a lens barrel with a quadrangular cross section and the like.
Therefore, in view of such technical problems, it is an object of the present invention to provide a lens driving apparatus, a lens guiding mechanism, and an optical instrument which are capable of carrying out power-changing and focusing operations by use of a single driving source and driving mechanism, and a lens driving apparatus which can be made smaller.
For achieving such an object, the present invention provides a lens driving apparatus used in a zoom lens optical system having at least a front group lens and a rear group lens, in which the front group lens and the rear group lens are moved along an optical axis for power changing and focusing, the lens driving apparatus comprising: an intermediate barrel movable along the optical axis of the optical system; a movable barrel, containing the front group lens, movable along the optical axis so as to retract or protrude with respect to the intermediate barrel as the intermediate barrel moves; and movable barrel moving means constituted by two link pieces intersecting each other at an axially supported intersecting part, a front end of the link pieces being attached to the movable barrel, a rear end of the link pieces being attached to the intermediate barrel, the movable barrel moving means being adapted to expand and contract as the intermediate barrel moves, so as to move the movable barrel along the optical axis.
According to this aspect of the present invention, if the intermediate barrel and the movable barrel are retracted into a collapsed state, then each link piece of the movable barrel moving means is collapsed, so as to reduce its size in the optical axis direction. As a consequence, optical instruments can be made smaller.
The lens driving apparatus in accordance with the present invention may comprise rear group lens moving means, pivotally attached to the movable barrel, for moving the rear group lens along the optical axis in synchronization with a movement of the movable barrel.
This configuration makes it possible to move the rear group lens differently from the movable barrel. Consequently, the distance between the rear group lens and the front group lens can be adjusted, so as to carry out an appropriate power-changing operation.
In the lens driving apparatus in accordance with the present invention, it is desirable that a fixed barrel from/into which the intermediate barrel is protruded/retracted be provided with a cam plate, the cam plate be formed with a cam groove which is oblique with respect to the optical axis, and the rear end of one of the link pieces engage the cam groove. This configuration makes it possible for the amount of movement of the movable barrel caused by the movement of the intermediate barrel to be set arbitrarily by the cam groove, whereby the lens position optimal for zoom focus control can be set.
Also, the present invention provides a lens driving apparatus used in a zoom lens optical system having at least a front group lens and a rear group lens, in which the front group lens and the rear group lens are moved along an optical axis for power changing and focusing, the lens driving apparatus comprising: an intermediate barrel movable along the optical axis; intermediate barrel moving means for moving the intermediate barrel along the optical axis; a movable barrel, containing the front group lens, adapted to retract or protrude with respect to the intermediate barrel in synchronization with a movement of the intermediate barrel; a rear group lens frame, containing the rear group lens, disposed so as to be movable along the optical axis; rear group lens moving means for moving the rear group lens frame along the optical axis in synchronization with a movement of the movable barrel; and rear group lens holding means for breaking the synchronization between the intermediate barrel and the movable barrel in a predetermined movement range when the intermediate barrel is moved in an opposite direction, so as to hold the rear group lens frame with respect to the intermediate barrel.
The lens driving apparatus in accordance with the present invention may be configured such that the intermediate barrel is moved in a predetermined direction for power changing and an opposite direction for focusing.
According to these aspects of the present invention, while the rear group lens moves along the optical axis in synchronization with a movement of the intermediate barrel, the rear group lens will move together with the intermediate barrel as being held thereby if the intermediate barrel is moved in the opposite direction. As a consequence, the distance between the rear group lens and the front group lens can be adjusted by a single driving mechanism and driving means for driving the intermediate barrel, such that a locus different from that for power changing is attained so as to enable appropriate focusing.
The present invention provides a lens guiding mechanism in a zoom lens optical system in which at least a front group lens and a rear group lens are moved along an optical axis for power changing and focusing, the lens guiding mechanism comprising: a guide axis, oriented in parallel with the optical axis, having a surface formed with a plurality of grooves at a predetermined interval; a front group lens container, containing the front group lens, movable along the guide axis; a rear group lens container, containing the rear group lens, supported so as to be movable within a predetermined range in the optical axis direction with respect to the front group lens container; and holding means, installed in the rear group lens container, for elastically pressing the surface of the guide axis, so as to hold the rear group lens container at a groove position.
According to this aspect of the present invention, if the front group lens container is moved along the guide axis, then the rear group lens container moves along therewith. As the front group lens container is moved, the rear group lens container can be moved to a groove position of the guide axis and can be held to the guide axis with the aid of the holding means, so as to allow the optical system to change its power. Also, if the front group lens container is moved in this state, then the front group lens moves toward or away from the rear group lens, whereby focusing of the optical system can be carried out. Therefore, a single driving source enables stepwise zooming.
The present invention provides an optical instrument having a zoom lens optical system in which at least a front group lens and a rear group lens are moved along an optical axis for power changing and focusing, the optical instrument comprising: a first guide axis, oriented in parallel with the optical axis, having a surface formed with a groove oriented to intersect the optical axis; a front group lens container, containing the front group lens, movable along the first guide axis; a rear group lens container, containing the rear group lens and comprising a presser for elastically pressing the surface of the first guide axis, movable along the optical axis; and rear group lens moving means, installed in the front group lens container, movable together with the front group lens container; the rear group lens moving means applying, along with a movement thereof, a moving force for moving the rear group lens container along the optical axis to the rear group lens container and applying no moving force to the rear group lens container within a predetermined movement range when a direction of movement thereof changes.
According to this aspect of the present invention, if the presser engages the groove of the first guide axis while the rear group lens container is held by the first guide, then the amount of movement of the front group lens and that of the rear group lens can be made different from each other. Therefore, the power of the optical system can be changed by moving the front group lens container along the guide axis, and focusing of the optical system can be carried out by shifting the rear group lens in the moving direction of the front group lens container thereafter so as to move the rear group lens toward or away from the front group lens. Hence, a single driving source and driving mechanism for driving the front group lens container enables appropriate power changing and focusing of the optical system.
The optical instrument in accordance with the present invention may comprise a second guide axis, installed in the front group lens container, for guiding the rear group lens container in parallel with the optical axis, the presser of the rear group lens container being disposed between the first guide axis and the second guide axis.
This configuration makes it possible for the second guide axis to receive the reaction force of the presser for pressing the first guide axis. As a consequence, rotational forces about the second guide axis can be prevented from applying to the rear group lens container, whereby the rear group lens container can appropriately be moved along the optical axis.